read/write file

操作フォルダ

#include

int main(void)
{
    char filename[100];
    static int num=1;
    snprintf(filename,100,"day_%d",num);
    FILE* fp;
    fp = fopen(filename,"rb");
    if(!fp){
        printf("error open fp
");
    }
    fseek(fp,20,SEEK_SET);
    //fseek(fp,0,SEEK_END);
    int len = ftell(fp);
    char buffer[100];
    fseek(fp,0,SEEK_SET);
    fread(buffer,len,1,fp);
    fclose(fp);

    FILE* fp_r;
    fp_r = fopen("day","w");
    if(!fp_r){
        printf("error open fp_r
");
    }
    fwrite(buffer,len,1,fp_r);
    fclose(fp_r);

    return 0;
}

2)

int main(int argc, char* argv[])
{
	char *read = (char *)malloc(100);
	FILE *fp;
	fp = fopen("a.txt","a+");//contain "Julie"
	if(fp == NULL)
		printf("fopen error
");
	//fread related with the fp location
	fseek(fp,0,SEEK_SET);
	if(fread(read,5,1,fp)!=1)
		printf("fread error
");
	sprintf(read+5,"%.14s","love me tender");
	int len = ftell(fp);
	if(len){
		printf("now the length is %d
",len);
		fseek(fp,0,SEEK_END);
	}
	//fwrite not related with fp location
	if(fwrite(read,strlen(read),1,fp)!=1)
		printf("fwrite failed
");

	printf("%s",read);
	printf("
");
	fclose(fp);
	return 0;
}