文件指针操作2

• 主要使用的函数
  功能比较强悍的主要就是fseek()函数了
  int fseek(FILE * pf, long offset, int WHENCE)
• 主要使用的场景
  1. 移动到文件中的指定位置,替换该位置的数据
  2. 在文件中遍历搜索给定的元素, 并替换该位置的数据
• 如下一个小demo,集合了需求的测试
  #include
#include
#include
void fseek_test(FILE * pf); void printf_file(FILE * pf, int size); int search_and_replace(FILE * pf, int size,double beReplaced, double replace);
int main(void){
char * path = "E:/test.bin";
FILE * pf;
pf = fopen(path, "wb+");
if(pf == NULL){
perror("open file err");
return -1;
}
fseek_test(pf);
if(pf != NULL){
fclose(pf);
}
getchar();
return 0;
}
void fseek_test(FILE *pf){
double src[10] = {0.1, 0.2, 0.3, 0.4, 0.5, 1.6, 1.7, 1.8,1.9, 2.0};
int rct = fwrite(src, sizeof(double), 10, pf);
if(rct != 10){
perror("write data err");
clearerr(pf);
return;
}
printf("%s\n", "first the data in the file:"); printf_file(pf, 10); fseek(pf, 0 - 3 *sizeof(double), SEEK_END); double tmp = 18.1; fwrite(&tmp, sizeof(double), 1, pf); printf("%s\n", "change the eight double to 18.1:"); printf_file(pf, 10); if(search_and_replace(pf, 10, 0.5, 100.1) >= 0){
printf("%s\n", "seach double 0.5 and replace it to 100.1,then show all number");
printf_file(pf, 10);
} }
// param pf : 文件指针 // @param size : 元素总个数 // @param beReplaced : 在文件中需要搜索的并且需要被替换的元素 // @param replace : 需要被替换为的结果元素
int search_and_replace(FILE * pf, int size, double beReplaced, double replace){
rewind(pf);
int i;
int retVal = -1;
double tmp = 0;
for(i = 0; i
int ret = fread(&tmp, sizeof(double), 1, pf);
if(ret == 1 && tmp == beReplaced){
fseek(pf, 0 - sizeof(double), SEEK_CUR);
tmp = replace;
fwrite(&tmp, sizeof(double), 1, pf);
retVal = i;
break;
}
}
return retVal;
}
// @param pf : 文件指针 // @param size : 文件中元素的个数
void printf_file(FILE * pf, int size){
rewind(pf);
double * src = ( double * ) malloc(sizeof(double) * size);
memset(src, 0, sizeof(double) * size);
int ret = fread(src, sizeof(double), size, pf);
if(ret != size){
perror("read file err");
clearerr(pf);
free(src);
return;
}
int i;
for(i = 0; i
printf("%f\t",src[i]);
if((i + 1)%2 == 0 && i != 0){
printf("\n");
}
}
free(src);
rewind(pf);
return;
}