在之前的文章《生信（五）awk求取某一列的平均值》中，笔者曾经给出过c语言求取某列平均值的代码，但是最近回顾时发现，这段代码至少有几点不足：
1. 利用 fgetc 函数来读取文件，现在看来效率不高。
2. 如果文件最后没有一个空白行的话，会陷入无限循环。也就是对 eof 的处理不完善。
大家都知道，c语言读取文件的常用函数有 fgetc、fgets、fread 以及 fscanf 等。笔者曾经一度以为就读取文件的效率而言，fgetc 不亚于其他函数。但是究竟是不是这样，还是自己验证一下让自己信服。
首先随机生成一个文件，1000万行，4列（该文件下面还会用到）。我们看一下上述函数读取文件的效率：
从上图中可以看出，fread 的效率最高，fgetc 的效率最低。当然这种比较很粗浅，但是能大概看出趋势。
各个函数读取文件的代码如下：其中 main 函数是一样的，只是 readfile 函数的实现不同。
#include <stdio.h> #include <stdlib.h> #include <time.h> #define bufsize 4096 void readfile(file* fp); int main(int argc, char* argv[]) { file *fp; time_t start, end; start = time(null); if (argc < 2) { printf("usage: %s <filename>\n", argv[0]); return 1; } if ((fp = fopen(argv[1], "r")) == null) { printf("error: cannot open file\n"); return 1; } readfile(fp); fclo(fp); end = time(null); printf("time spent: %d conds\n", end - start); return 0; } // readfile_fgetc: void readfile(file* fp) { char c; while ((c = fgetc(fp)) != eof) ; } // readfile_fgets: void readfile(file* fp) { char buf[bufsize]; while (fgets(buf, maxline, fp) != null) ; } // readfile_fread: void rea中国婚纱品牌dfile(file* fp) { char buf[bufsize]; while (fread(buf, 1, bufsize, fp) > 0) ; } // readfile_fscanf: void readfile(file* fp) { char buf[bufsize]; while (fscanf(fp, " %[^\n]s", buf) == 1) ; }那么各个函数计算列平均值的效率如何呢？我们依然使用上面那1000万行的文件，用上述各个函数实现计算第2列平均数的功能，它们的效率如下：
代码如下：main 函数大体上是一样的，只是 colaver 函数的实现不一样。
（这些代码完善地处理了eof，无论文件最后是否有空白行都可以正确运行。但是仍然有前提，就是文件中每一行的分隔符（列数）是一样的，否则代码可能会出错。）
这些代码中，fscanf 的最简短，该函数可以大大提高格式化读取数据的编程效率。
#include <stdio.h>#include <stdlib.h>#include <time.h>#define bufsize 4096void getcolaver(file* fp, const int k); int main(int argc, char* argv[]) { file *fp; time_t start, end; start = time(null); if (argc < 2) { printf("usage: %s <filename>\n", argv[0]); return 1; } if ((fp = fopen(argv[1], "r")) == null) { printf("error: cannot open file\n"); return 1; } getcolaver(fp, 2); fclo(fp); end = time(null); printf("time spent: %d conds\n", end - start); return 0; } // colaver_fgetc: void getcolaver(file* fp, const int k) { int i = 0; // num of '\t' int j = 0; // num of chars int c; // char char col[50]; float sum = 0; int n = 0; // num of lines. int incol = 0; while ((c = fgetc(fp)) != eof) { if (i == k - 1) { incol = 1; if (c == '\t') i++; el if (c == '\n') i = 0; el col[j++] = c; } el { if (c == '\t') i++; el if (c == '\n') i = 0; if (incol) { col[j] = '#include <stdio.h>#include <stdlib.h>#include <time.h>#define bufsize 4096void getcolaver(file* fp, const int k);int main(int argc, char* argv[]) {file *fp;time_t start, end;start = time(null);if (argc < 2) {printf("usage: %s <filename>\n", argv[0]);return 1;}if ((fp = fopen(argv[1], "r")) == null) {printf("error: cannot open file\n");return 1;}getcolaver(fp, 2);fclo(fp);end = time(null);printf("time spent: %d conds\n", end - start);return 0;}// colaver_fgetc:void getcolaver(file* fp, const int k) {int i = 0; // num of '\t'int j = 0; // num of charsint c; // charchar col[50];float sum = 0;int n = 0; // num of lines.int incol = 0;while ((c = fgetc(fp)) != eof) {if (i == k - 1) {incol = 1;if (c == '\t') i++;el if (c == '\n') i = 0;el col[j++] = c;} el {if (c == '\t') i++;el if (c == '\n') i = 0;if (incol) {col[j] = '\0';sum += atof(col);n++;}j = 0;incol = 0;}}if (incol) {col[j] = '\0';sum += atof(col);n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col %d is %f\n", k, sum / n);}// colaver_fgets:void getcolaver(file* fp, const int k) {int i = 0; // num of '\t'int j = 0; // num of charschar col[50];char buf[bufsize];float sum = 0;int n = 0; // num of lines.int incol = 0;char* p;while (fgets(buf, bufsize, fp) != null) {for (p = buf; *p != '\0'; p++) {if (i == k - 1) {incol = 1;if (*p == '\t') i++;el if (*p == '\n') i = 0;el col[j++] = *p;} el {if (*p == '\t') i++;el if (*p == '\n') i = 0;if (incol) {col[j] = '\0';sum += atof(col);n++;}j = 0;incol = 0;}}}if (incol) {col[j] = '\0';sum += atof(col);n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col %d is %f\n", k, sum / n);}// colaver_fread:void getcolaver(file* fp, const int k) {int i = 0; // num of '\t'int j = 0; // num of charschar col[50];char buf[bufsize];float sum = 0;int n = 0; // num of lines.int m, l;int sizechr = sizeof(char);int incol = 0;while ((l = fread(buf, sizechr, bufsize, fp)) > 0) {for (m = 0; m < l; m++) {if (i == k - 1) {incol = 1;if (buf[m] == '\t') i++;el if (buf[m] == '\n') i = 0;el col[j++] = buf[m];} el {if (buf[m] == '\t') i++;el if (buf[m] == '\n') i = 0;if (incol) {col[j] = '\0';sum += atof(col);n++;}j = 0;incol = 0;}}}if (incol) {col[j] = '\0';sum += atof(col);n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col %d is %f\n", k, sum / n);}// colaver_fscanf:void getcolaver(file* fp) {float f;float sum = 0;int n = 0; // num of lines.while (fscanf(fp, "%*s%f%*[^\n]s", &f) == 1) {sum += f;n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col 2 is %f\n", sum / n);}'; sum += atof(col); n++; } j = 0; incol = 0; } } if (incol) { col[j] = '#include <stdio.h>#include <stdlib.h>#include <time.h>#define bufsize 4096void getcolaver(file* fp, const int k);int main(int argc, char* argv[]) {file *fp;time_t start, end;start = time(null);if (argc < 2) {printf("usage: %s <filename>\n", argv[0]);return 1;}if ((fp = fopen(argv[1], "r")) == null) {printf("error: cannot open file\n");return 1;}getcolaver(fp, 2);fclo(fp);end = time(null);printf("time spent: %d conds\n", end - start);return 0;}// colaver_fgetc:void getcolaver(file* fp, const int k) {int i = 0; // num of '\t'int j = 0; // num of charsint c; // charchar col[50];float sum = 0;int n = 0; // num of lines.int incol = 0;while ((c = fgetc(fp)) != eof) {if (i == k - 1) {incol = 1;if (c == '\t') i++;el if (c == '\n') i = 0;el col[j++] = c;} el {if (c == '\t') i++;el if (c == '\n') i = 0;if (incol) {col[j] = '\0';sum += atof(col);n++;}j = 0;incol = 0;}}if (incol) {col[j] = '\0';sum += atof(col);n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col %d is %f\n", k, sum / n);}// colaver_fgets:void getcolaver(file* fp, const int k) {int i = 0; // num of '\t'int j = 0; // num of charschar col[50];char buf[bufsize];float sum = 0;int n = 0; // num of lines.int incol = 0;char* p;while (fgets(buf, bufsize, fp) != null) {for (p = buf; *p != '\0'; p++) {if (i == k - 1) {incol = 1;if (*p == '\t') i++;el if (*p == '\n') i = 0;el col[j++] = *p;} el {if (*p == '\t') i++;el if (*p == '\n') i = 0;if (incol) {col[j] = '\0';sum += atof(col);n++;}j = 0;incol = 0;}}}if (incol) {col[j] = '\0';sum += atof(col);n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col %d is %f\n", k, sum / n);}// colaver_fread:void getcolaver(file* fp, const int k) {int i = 0; // num of '\t'int j = 0; // num of charschar col[50];char buf[bufsize];float sum = 0;int n = 0; // num of lines.int m, l;int sizechr = sizeof(char);int incol = 0;while ((l = fread(buf, sizechr, bufsize, fp)) > 0) {for (m = 0; m < l; m++) {if (i == k - 1) {incol = 1;if (buf[m] == '\t') i++;el if (buf[m] == '\n') i = 0;el col[j++] = buf[m];} el {if (buf[m] == '\t') i++;el if (buf[m] == '\n') i = 0;if (incol) {col[j] = '\0';sum += atof(col);n++;}j = 0;incol = 0;}}}if (incol) {col[j] = '\0';sum += atof(col);n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col %d is %f\n", k, sum / n);}// colaver_fscanf:void getcolaver(file* fp) {float f;float sum = 0;int n = 0; // num of lines.while (fscanf(fp, "%*s%f%*[^\n]s", &f) == 1) {sum += f;n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col 2 is %f\n", sum / n);}'; sum += atof(col); n++; } if (n == 0) printf("error: no line!\n"); el printf("the average of col %d is %f\n", k, sum / n); } // colaver_fgets: void getcolaver(file* fp, const int k) { int i = 0; // num of '\t' int j = 0; // num of chars char col[50]; char buf[bufsize]; float sum = 0; int n = 0; // num of lines. int incol = 0; char* p; while (fgets(buf, bufsize, fp) != null) { for (p = buf; *p != '#include <stdio.h>#include <stdlib.h>#include <time.h>#define bufsize 4096void getcolaver(file* fp, const int k);int main(int argc, char* argv[]) {file *fp;time_t start, end;start = time(null);if (argc < 2) {printf("usage: %s <filename>\n", argv[0]);return 1;}if ((fp = fopen(argv[1], "r")) == null) {printf("error: cannot open file\n");return 1;}getcolaver(fp, 2);fclo(fp);end = time(null);printf("time spent: %d conds\n", end - start);return 0;}// colaver_fgetc:void getcolaver(file* fp, const int k) {int i = 0; // num of '\t'int j = 0; // num of charsint c; // charchar col[50];float sum = 0;int n = 0; // num of lines.int incol = 0;while ((c = fgetc(fp)) != eof) {if (i == k - 1) {incol = 1;if (c == '\t') i++;el if (c == '\n') i = 0;el col[j++] = c;} el {if (c == '\t') i++;el if (c == '\n') i = 0;if (incol) {col[j] = '\0';sum += atof(col);n++;}j = 0;incol = 0;}}if (incol) {col[j] = '\0';sum += atof(col);n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col %d is %f\n", k, sum / n);}// colaver_fgets:void getcolaver(file* fp, const int k) {int i = 0; // num of '\t'int j = 0; // num of charschar col[50];char buf[bufsize];float sum = 0;int n = 0; // num of lines.int incol = 0;char* p;while (fgets(buf, bufsize, fp) != null) {for (p = buf; *p != '\0'; p++) {if (i == k - 1) {incol = 1;if (*p == '\t') i++;el if (*p == '\n') i = 0;el col[j++] = *p;} el {if (*p == '\t') i++;el if (*p == '\n') i = 0;if (incol) {col[j] = '\0';sum += atof(col);n++;}j = 0;incol = 0;}}}if (incol) {col[j] = '\0';sum += atof(col);n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col %d is %f\n", k, sum / n);}// colaver_fread:void getcolaver(file* fp, const int k) {int i = 0; // num of '\t'int j = 0; // num of charschar col[50];char buf[bufsize];float sum = 0;int n = 0; // num of lines.int m, l;int sizechr = sizeof(char);int incol = 0;while ((l = fread(buf, sizechr, bufsize, fp)) > 0) {for (m = 0; m < l; m++) {if (i == k - 1) {incol = 1;if (buf[m] == '\t') i++;el if (buf[m] == '\n') i = 0;el col[j++] = buf[m];} el {if (buf[m] == '\t') i++;el if (buf[m] == '\n') i = 0;if (incol) {col[j] = '\0';sum += atof(col);n++;}j = 0;incol = 0;}}}if (incol) {col[j] = '\0';sum += atof(col);n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col %d is %f\n", k, sum / n);}// colaver_fscanf:void getcolaver(file* fp) {float f;float sum = 0;int n = 0; // num of lines.while (fscanf(fp, "%*s%f%*[^\n]s", &f) == 1) {sum += f;n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col 2 is %f\n", sum / n);}'; p++) { if (i == k - 1) { incol = 1; if (*p == '\t') i++; el if (*p == '\n') i = 0; el col[j++] = *p; } el { if (*p == '\t') i++; el if (*p == '\n') i = 0; if (incol) { col[j] = '#include <stdio.h>#include <stdlib.h>#include <time.h>#define bufsize 4096void getcolaver(file* fp, const int k);int main(int argc, char* argv[]) {file *fp;time_t start, end;start = time(null);if (argc < 2) {printf("usage: %s <filename>\n", argv[0]);return 1;}if ((fp = fopen(argv[1], "r")) == null) {printf("error: cannot open file\n");return 1;}getcolaver(fp, 2);fclo(fp);end = time(null);printf("time spent: %d conds\n", end - start);return 0;}// colaver_fgetc:void getcolaver(file* fp, const int k) {int i = 0; // num of '\t'int j = 0; // num of charsint c; // charchar col[50];float sum = 0;int n = 0; // num of lines.int incol = 0;while ((c = fgetc(fp)) != eof) {if (i == k - 1) {incol = 1;if (c == '\t') i++;el if (c == '\n') i = 0;el col[j++] = c;} el {if (c == '\t') i++;el if (c == '\n') i = 0;if (incol) {col[j] = '\0';sum += atof(col);n++;}j = 0;incol = 0;}}if (incol) {col[j] = '\0';sum += atof(col);n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col %d is %f\n", k, sum / n);}// colaver_fgets:void getcolaver(file* fp, const int k) {int i = 0; // num of '\t'int j = 0; // num of charschar col[50];char buf[bufsize];float sum = 0;int n = 0; // num of lines.int incol = 0;char* p;while (fgets(buf, bufsize, fp) != null) {for (p = buf; *p != '\0'; p++) {if (i == k - 1) {incol = 1;if (*p == '\t') i++;el if (*p == '\n') i = 0;el col[j++] = *p;} el {if (*p == '\t') i++;el if (*p == '\n') i = 0;if (incol) {col[j] = '\0';sum += atof(col);n++;}j = 0;incol = 0;}}}if (incol) {col[j] = '\0';sum += atof(col);n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col %d is %f\n", k, sum / n);}// colaver_fread:void getcolaver(file* fp, const int k) {int i = 0; // num of '\t'int j = 0; // num of charschar col[50];char buf[bufsize];float sum = 0;int n = 0; // num of lines.int m, l;int sizechr = sizeof(char);int incol = 0;while ((l = fread(buf, sizechr, bufsize, fp)) > 0) {for (m = 0; m < l; m++) {if (i == k - 1) {incol = 1;if (buf[m] == '\t') i++;el if (buf[m] == '\n') i = 0;el col[j++] = buf[m];} el {if (buf[m] == '\t') i++;el if (buf[m] == '\n') i = 0;if (incol) {col[j] = '\0';sum += atof(col);n++;}j = 0;incol = 0;}}}if (incol) {col[j] = '\0';sum += atof(col);n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col %d is %f\n", k, sum / n);}// colaver_fscanf:void getcolaver(file* fp) {float f;float sum = 0;int n = 0; // num of lines.while (fscanf(fp, "%*s%f%*[^\n]s", &f) == 1) {sum += f;n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col 2 is %f\n", sum / n);}'; sum += atof(col); n++; } j = 0; incol = 0; } } } if (incol) { col[j] = '#include <stdio.h>#include <stdlib.h>#include <time.h>#define bufsize 4096void getcolaver(file* fp, const int k);int main(int argc, char* argv[]) {file *fp;time_t start, end;start = time(null);if (argc < 2) {printf("usage: %s <filename>\n", argv[0]);return 1;}if ((fp = fopen(argv[1], "r")) == null) {printf("error: cannot open file\n");return 1;}getcolaver(fp, 2);野火烧不尽春风吹又生fclo(fp);end = time(null);printf("time spent: %d conds\n", end - start);return 0;}// colaver_fgetc:void getcolaver(file* fp, const int k) {int i = 0; // num of '\t'int j = 0; // num of charsint c; // charchar col[50];float sum = 0;int n = 0; // num of lines.int incol = 0;while ((c = fgetc(fp)) != eof) {if (i == k - 1) {incol = 1;if (c == '\t') i++;el if (c == '\n') i = 0;el col[j++] = c;} el {if (c == '\t') i++;el if (c == '\n') i = 0;if (incol) {col[j] = '\0';sum += atof(col);n++;}j = 0;incol = 0;}}if (incol) {col[j] = '\0';sum += atof(col);n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col %d is %f\n", k, sum / n);}// colaver_fgets:void getcolaver(file* fp, const int k) {int i = 0; // num of '\t'int j = 0; // num of charschar col[50];char buf[bufsize];float sum = 0;int n = 0; // num of lines.int incol = 0;char* p;while (fgets(buf, bufsize, fp) != null) {for (p = buf; *p != '\0'; p++) {if (i == k - 1) {incol = 1;if (*p == '\t') i++;el if (*p == '\n') i = 0;el col[j++] = *p;} el {if (*p == '\t') i++;el if (*p == '\n') i = 0;if (incol) {col[j] = '\0';sum += atof(col);n++;}j = 0;incol = 0;}}}if (incol) {col[j] = '\0';sum += atof(col);n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col %d is %f\n", k, sum / n);}// colaver_fread:void getcolaver(file* fp, const int k) {int i = 0; // num of '\t'int j = 0; // num of charschar col[50];char buf[bufsize];float sum = 0;int n = 0; // num of lines.int m, l;int sizechr = sizeof(char);int incol = 0;while ((l = fread(buf, sizechr, bufsize, fp)) > 0) {for (m = 0; m < l; m++) {if (i == k - 1) {incol = 1;if (buf[m] == '\t') i++;el if (buf[m] == '\n') i = 0;el col[j++] = buf[m];} el {if (buf[m] == '\t') i++;el if (buf[m] == '\n') i = 0;if (incol) {col[j] = '\0';sum += atof(col);n++;}j = 0;incol = 0;}}}if (incol) {col[j] = '\0';sum += atof(col);n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col %d is %f\n", k, sum / n);}// colaver_fscanf:void getcolaver(file* fp) {float f;float sum = 0;int n = 0; // num of lines.while (fscanf(fp, "%*s%f%*[^\n]s", &f) == 1) {sum += f;n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col 2 is %f\n", sum / n);}'; sum += atof(col); n++; } if (n == 0) printf("error: no line!\n"); el printf("the average of col %d is %f\n", k, sum / n); } // colaver_fread: void getcolaver(file* fp, const int k) { int i = 0; // num of '\t' int j = 0; // num of chars char col[50]; char buf[bufsize]; float sum = 0; int n = 0; // num of lines. int m, l; int sizechr = sizeof(char); int incol = 0; while ((l = fread(buf, sizechr, bufsize, fp)) > 0) { for (m = 0; m < l; m++) { if (i == k - 1) { incol = 1; if (buf[m] == '\t') i++; el if (buf[m] == '\n') i = 0; el col[j++] = buf[m]; } el { if (buf[m] == '\t') i++; el if (buf[m] == '\n') i = 0; if (incol) { col[j] = '#include <stdio.h>#include <stdlib.h>#include <time.h>#define bufsize 4096void getcolaver(file* fp, const int k);int main(int argc, char* argv[]) {file *fp;time_t start, end;start = time(null);if (argc < 2) {printf("usage: %s <filename>\n", argv[0]);return 1;}if ((fp = fopen(argv[1], "r")) == null) {printf("error: cannot open file\n");return 1;}getcolaver(fp, 2);fclo(fp);end = time(null);printf("time spent: %d conds\n", end - start);return 0;}// colaver_fgetc:void getcolaver(file* fp, const int k) {int i = 0; // num of '\t'int j = 0; // num of charsint c; // charchar col[50];float sum = 0;int n = 0; // num of lines.int incol = 0;while ((c = fgetc(fp)) != eof) {if (i == k - 1直播 百花奖颁奖典礼) {incol = 1;if (c == '\t') i++;el if (c == '\n') i = 0;el col[j++] = c;} el {if (c == '\t') i++;el if (c == '\n') i = 0;if (incol) {col[j] = '\0';sum += atof(col);n++;}j = 0;incol = 0;}}if (incol) {col[j] = '\0';sum += atof(col);n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col %d is %f\n", k, sum / n);}// colaver_fgets:void getcolaver(file* fp, const 寒冰女巫出装int k) {int i = 0; // num of '\t'int j = 0; // num of charschar col[50];char buf[bufsize];float sum = 0;int n = 0; // num of lines.int incol = 0;char* p;while (fgets(buf, bufsize, fp) != null) {for (p = buf; *p != '\0'; p++) {if (i == k - 1) {incol = 1;if (*p == '\t') i++;el if (*p == '\n') i = 0;el col[j++] = *p;} el {if (*p == '\t') i++;el if (*p == '\n') i = 0;if (incol) {col[j] = '\0';sum += atof(col);n++;}j = 0;incol = 0;}}}if (incol) {col[j] = '\0';sum += atof(col);n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col %d is %f\n", k, sum / n);}// colaver_fread:void getcolaver(file* fp, const int k) {int i = 0; // num of '\t'int j = 0; // num of charschar col[50];char buf[bufsize];float sum = 0;int n = 0; // num of lines.int m, l;int sizechr = sizeof(char);int incol = 0;while ((l = fread(buf, sizechr, bufsize, fp)) > 0) {for (m = 0; m < l; m++) {if (i == k - 1) {incol = 1;if (buf[m] == '\t') i++;el if (buf[m] == '\n') i = 0;el col[j++] = buf[m];}小伙伴们惊呆了 el {if (buf[m] == '\t') i++;el if (buf[m] == '\n') i = 0;if (incol) {col[j] = '\0';sum += atof(col);n++;}j = 0;incol = 0;}}}if (incol) {col[j] = '\0';sum += atof(col);n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col %d is %f\n", k, sum / n);}// colaver_fscanf:void getcolaver(file* fp) {float f;float sum = 0;int n = 0; // num of lines.while (fscanf(fp, "%*s%f%*[^\n]s", &f) == 1) {sum += f;n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col 2 is %f\n", sum / n);}'; sum += atof(col); n++; } j = 0; incol = 0; } } } if (incol) { col[j] = '#include <stdio.h>#include <stdlib.h>#include <time.h>#define bufsize 4096void getcolaver(file* fp, const int k);int main(int argc, char* argv[]) {file *fp;time_t start, end;start = time(null);if (argc < 2) {printf("usage: %s <filename>\n", argv[0]);return 1;}if ((fp = fopen(argv[1], "r")) == null) {printf("error: cannot open file\n");return 1;}getcolaver(fp, 2);fclo(fp);end = time(null);printf("time spent: %d conds\n", end - start);return 0;}// colaver_fgetc:void getcolaver(file* fp, const int k) {int i = 0; // num of '\t'int j = 0; // num of charsint c; // charchar col[50];float sum = 0;int n = 0; // num of lines.int incol = 0;while ((c = fgetc(fp)) != eof) {if (i == k - 1) {incol = 1;if (c == '\t') i++;el if (c == '\n') i = 0;el col[j++] = c;} el {if (c == '\t') i++;el if (c == '\n') i = 0;if (incol) {col[j] = '\0';sum += atof(col);n++;}j = 0;incol = 0;}}if (incol) {col[j] = '\0';sum += atof(col);n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col %d is %f\n", k, sum / n);}// colaver_fgets:void getcolaver(file* fp, const int k) {int i = 0; // num of '\t'int j = 0; // num of charschar col[50];char buf[bufsize];float sum = 0;int n = 0; // num of lines.int incol = 0;char* p;while (fgets(buf, bufsize, fp) != null) {for (p = buf; *p != '\0'; p++) {if (i == k - 1) {incol = 1;if (*p == '\t') i++;el if (*p == '\n') i = 0;el col[j++] = *p;} el {if (*p == '\t') i++;el if (*p == '\n') i = 0;if (incol) {col[j] = '\0';sum += atof(col);n++;}j = 0;incol = 0;}}}if (incol) {col[j] = '\0';sum += atof(col);n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col %d is %f\n", k, sum / n);}// colaver_fread:void getcolaver(file* fp, const int k) {int i = 0; // num of '\t'int j = 0; // num of charschar col[50];char buf[bufsize];float sum = 0;int n = 0; // num of lines.int m, l;int sizechr = sizeof(char);int incol = 0;while ((l = fread(buf, sizechr, bufsize, fp)) > 0) {for (m = 0; m < l; m++) {if (i == k - 1) {incol = 1;if (buf[m] == '\t') i++;el if (buf[m] == '\n') i = 0;el col[j++] = buf[m];} el {if (buf[m] == '\t') i++;el if (buf[m] == '\n') i = 0;if (incol) {col[j] = '\0';sum += atof(col);n++;}j = 0;incol = 0;}}}if (incol) {col[j] = '\0';sum += atof(col);n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col %d is %f\n", k, sum / n);}// colaver_fscanf:void getcolaver(file* fp) {float f;float sum = 0;int n = 0; // num of lines.while (fscanf(fp, "%*s%f%*[^\n]s", &f) == 1) {sum += f;n++;}if (n == 0) printf("error: no line!\n");el printf("the average of col 2 is %f\n", sum / n);}'; sum += atof(col); n++; } if (n == 0) printf("error: no line!\n"); el printf("the average of col %d is %f\n", k, sum / n); } // colaver_fscanf: void getcolaver(file* fp) { float f; float sum = 0; int n = 0; // num of lines. while (fscanf(fp, "%*s%f%*[^\n]s", &f) == 1) { sum += f; n++; } if (n == 0) printf("error: no line!\n"); el printf("the average of col 2 is %f\n", sum / n); }以上就是详解c语言读取文件求某一列的平均值的详细内容，更多关于c语言读取文件求某一列的平均值的资料请关注www.887551.com其它相关文章！
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