问题见：关于C语言fprinf的一个问题
从头开始fprintf覆写是可以的
#include <stdio.h>
int main(){
char *str = "STUDENTS";
FILE *fp;
if ((fp=fopen("d.txt", "r+")) == NULL){
printf("\a打开文件失败！\n");
return 1;
}
printf("%ld",ftell(fp)); //输出为0
fprintf(fp, "%s",str); //正常覆写
fclose(fp);
return 0;
}
/* d.txt
We are students. All the students study very hard.
So, these students are outstanding students.
*/
/* result //正常覆写
STUDENTStudents. All the students study very hard.
So, these students are outstanding students.
*/
fgetc移动光标后就没有任何反应
#include <stdio.h>
int main(){
char *str = "STUDENTS";
FILE *fp;
if ((fp=fopen("d.txt", "r+")) == NULL){
printf("\a打开文件失败！\n");
return 1;
}
fgetc(fp);fgetc(fp);
fgetc(fp);fgetc(fp); //加了这个怎么就没反应了啊，覆写都不了？？？
printf("%ld",ftell(fp)); //输出为4
fprintf(fp, "%s",str); //文件没有任何变动
fclose(fp);
return 0;
}
/* d.txt
We are students. All the students study very hard.
So, these students are outstanding students.
*/
/* result //文件没有任何变动
We are students. All the students study very hard.
So, these students are outstanding students.
*/
用fseek移位后可以正常覆写
#include <stdio.h>
int main(){
char *str = "STUDENTS";
FILE *fp;
if ((fp=fopen("d.txt", "r+")) == NULL){
printf("\a打开文件失败！\n");
return 1;
}
printf("%ld",ftell(fp)); //输出为0
fseek(fp, 4, SEEK_SET);
printf("%ld",ftell(fp)); //输出为4
fprintf(fp, "%s",str); //正常覆写
fclose(fp);
return 0;
}
/* d.txt
We are students. All the students study very hard.
So, these students are outstanding students.
*/
/* result //移位后正常覆写
We aSTUDENTSnts. All the students study very hard.
So, these students are outstanding students.
*/
fgetc移位加上fseek也能正常覆写
#include <stdio.h>
int main(){
char *str = "STUDENTS";
FILE *fp;
if ((fp=fopen("d.txt", "r+")) == NULL){
printf("\a打开文件失败！\n");
return 1;
}
fgetc(fp);fgetc(fp);
fgetc(fp);fgetc(fp); //加了这个怎么就没反应了啊，覆写都不了？？？
printf("%ld",ftell(fp)); //输出为4
fseek(fp, ftell(fp), SEEK_SET); //用ftell保证原位
printf("%ld",ftell(fp)); //输出为4
fprintf(fp, "%s",str); //正常覆写
fclose(fp);
return 0;
}
/* d.txt
We are students. All the students study very hard.
So, these students are outstanding students.
*/
/* result //移位后正常覆写
We aSTUDENTSnts. All the students study very hard.
So, these students are outstanding students.
*/
但将fseek的手法拿到之前的程序还是照常错误。迷惑？？？
#include <stdio.h>
int match(FILE *fp, char *str);
void upper(FILE *fp, char *str);
int main(){
//获取输入
char path[81]={0}, str[32]={0};
int check;
printf("请输入文件名：");
check = scanf_s("%s", path, 81);
if (check==0){
printf("输入的文件名过长！\n");
return 1;
}
printf("请输入英文字符串：");
check = scanf_s("%s", str, 32);
if (check==0){
printf("输入的英文字符串过长！\n");
return 1;
}
//统一将字符串str大写化
char *c = str;
while (*c != '\0')
{
if (*c>='a' && *c<='z')
*c -= 32;
c++;
}
//打开文件
FILE *fp;
if ((fp=fopen(path, "r+")) == NULL){
printf("打开文件失败！\n");
return 1;
}
//读取文件并查找替换匹配的字符
do {
if (match(fp, str)){
fseek(fp, ftell(fp), SEEK_SET); //补一个这个也不行，具体为什么不知道
fprintf(fp, "%s", str);
continue; //已经移位了
}
fgetc(fp); //让光标移位到下一个
} while (!feof(fp));
fclose(fp);
return 0;
}
int match(FILE *fp, char *str){
int current = ftell(fp);
char *q=str, p=fgetc(fp);
int ret = -1; //默认-1用于判断是否被修改
while (*q!='\0' && p!=EOF)
{
p = p>='a'&&p<='z' ? p-32 : p;
if (*q != p) ret = 0; //在str或fp没结束就不匹配了
q++;
p = fgetc(fp);
}
if (*q=='\0' && ret==-1) ret = 1; //str结束前都是匹配的，所以匹配
else ret = 0; //否则是前面已判断或fp结束，不全匹配
//光标归位
fseek(fp, current, SEEK_SET);
return ret;
}
/* d.txt
We are students. All the students study very hard.
So, these students are outstanding students.
*/
//输入d.txt\nstudents
/* result //老问题
We are STUDENTSs. All th STUDENTSs study vry hard.
So, these STUDENTSs are outtanding STUDENTSs........
*/