为什么打印log(比如printf)会经常碰到core dump?

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在实际开发中，我们少不了打log, 如果参数类型和个数没有完全对应，那就等着core dump吧（更可怕的是不得不解决的低概率core dump），为什么呢？我们以printf为例来看看源码：

int printf(const char *fmt, ...){    char buf[1024];    va_list args;    int cnt;    va_start(args, fmt);    cnt = vsprintf(buf, fmt, args);    va_end(args);        putstr(buf);    return cnt;}

继续看vsprintf,

int vsprintf(char *buf, const char *fmt, va_list args){    char *str, *s;    int base;    int flags = 0;    int fildwidth = -1;    int precision = -1;    int qualifier;    unsigned long num;    for(str = buf; *fmt != '\0'; fmt++) {        if(*fmt == '\t') {            int k = 8;            while(k--)                *str++ = ' ';            fmt++;        }        if(*fmt != '%') {            *str++ = *fmt;            continue;        }handle_flags:        fmt++;        switch (*fmt) {            case '#':                    flags |= PREFIX;                    goto handle_flags;            }    /* handle_fldwidth: */        /* don't need this now */    /* handle_precision: */        /* don't need this now */    /* handle_lenmodifier: */        /* don't need this now */    /* handle_qualifier: */        qualifier = -1;        if(*fmt == 'l' || *fmt == 'L' || *fmt == 'h') {            qualifier = *fmt;            fmt++;        }    /* handle_convtype: */        base = 10;        switch(*fmt) {            case 'c':                /* processing alignment */                *str = (unsigned char)va_arg(args, int);                /* processing alignment */                continue;            case 's':                s = va_arg(args, char *);                str = strcpy(str, s);         /* is it safe? */                str--;                continue;            case 'd':                break;            case 'o':                    base = 8;                    break;            case 'x':                 flags |= SMALL;            case 'X':                base = 16;                break;            default:                *str++ = '%';                if(*fmt)                    *str++ = *fmt;                else                    fmt--;                continue;        }        if (qualifier == 'l')            num = va_arg(args, unsigned long);        else if (qualifier == 'h')                    num = (unsigned short)va_arg(args, int);        else {            num = va_arg(args, int);        }        str = num2str(str, num, base, fildwidth, precision, flags);    }    *str = '\0';    return str - buf;}

可见，参数个数、类型不匹配，会导致内存赋值错误， core dump也就来啦。

OK, 先说这么多，睡觉。

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