本文共 1058 字，大约阅读时间需要 3 分钟。

#include <stdio.h>#include <stdlib.h>#include <ctype.h>int main(int argc, char *args[]){    FILE *fp;    char *s, *sp;    int file_size, read_size;    if(argc != 2){        fprintf(stdout, "usage: change filename\n");        exit(EXIT_FAILURE);    }    if((fp = fopen(args[1], "rb+")) == NULL){        fprintf(stderr, "Can't open %s\n", args[1]);        exit(EXIT_FAILURE);            }        fseek(fp, 0L, SEEK_END);    //文件指针移动到文件末尾    file_size = ftell(fp);    rewind(fp); //文件指针移动到文件开头    //为字符数组分配内存，然后读入数据    s = (char *)calloc(file_size, 1);    read_size = fread(s, 1, file_size, fp);    fclose(fp);    if(read_size != file_size){        fprintf(stdout, "Can't read all massage!\n");        exit(EXIT_FAILURE);    }    //转换字母    sp = s;    while(*sp){        if(islower(*sp))            *sp = toupper(*sp);        sp++;    }    //先清除源文件数据，然后向文件写入字符数组数据    if((fp = fopen(args[1], "wb+")) == NULL){        fprintf(stderr, "Can't open %s\n", args[1]);        exit(EXIT_FAILURE);            }    fwrite(s, 1, read_size, fp);    fclose(fp);    return 0;}